Baryta paper has been conventionally used for photographic printing paper. However, after so-called water-resistant printing paper coated with polyolefin on both surfaces of base paper was invented for the purpose of allowing more rapidity in the developing treatment, such printing paper has become the predominant type of water-resistant photographic printing paper. Usually, such water-resistant printing paper has a photographic emulsion layer on one surface thereof (generally a polyolefin layer containing an inorganic pigment such as titanium oxide, TiO.sub.2).
It is desirable that the other surface to which an emulsion layer is not applied, that is, the back surface, has good properties for purposes of being subject to writing, drawing, and printing thereon for various purposes, by using a ball-point pen, a fountain pen, a pencil, with oil-based ink, water-based ink, or the like.
However, as described above, the water-resistant printing paper is coated with polyolefin, most popularly polyethylene. The surface of this paper is therefore hydrophobic and non-absorbent, and this paper is disadvantages, for example, in that it is difficult to write thereon with a pencil or fountain pen, in that the paper is apt to be damaged by writing thereon, and in that the record is apt to disappear or blot by slight rubbing after writing.
As a method for providing improved properties with respect to writing, drawing, printing, or the like, on a polyolefin layer, conventionally, there have been proposed, for example, a method of roughening the surface with sandblasting, embossing, or the like, or a method of roughening the surface by etching with acid, or the like. However, a polyolefin layer treated by such a method has no satisfactory property in writing.
In order to overcome these disadvantages, various methods have been proposed, e.g., as follows:
(1) A method of incorporating an inorganic pigment having an average diameter of from 1 to 40 .mu.m into a polyolefin resin layer on the back surface, as described in Japanese Patent Application (OPI) No. 43528/1980 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application");
(2) A method of providing a layer consisting of a water-soluble polymer, such as polyvinyl alcohol and carboxyl methyl cellulose, and water silica sol, as described in Japanese Patent Publication No. 14884/1969;
(3) A method of providing a layer consisting of a water-insoluble polymer emulsion, such as a polyethylene emulsion, and water silica sol, as described in Japanese Patent Publication No. 36565/1975; and
(4) A method of providing a coating layer including a pigment such as clay, and having a hygroscopic quality, as described in Japanese Utility Model Application Laid-Open No. 169426/1977.
However, each of these known methods has defects. For example, the method of incorporating from 1 to 40 .mu.m inorganic pigment into a polyolefin resin layer of a back surface is of little practical use, because of problems such as a poor quality due to breaking of the resin layer, staining pigment during the manufacturing process, etc. For the layer applied with the conventional compound, it is necessary to select the amount of application to be about 5 g/m.sup.2, or in some cases, 10 g/m.sup.2 or more, in order to provide good writing properties, particularly with respect to pencil writing. Therefore, the preparation of such coated layers has been restricted in many respects, for example, in regard to the drying step, etc.
With respect to defects in quality, disadvantages such as disjoining or elution of the applied layer, coloring in the applied layer by developing solutions, adhering of the coating layer with the surface, etc., occur, and no product fully satisfying the desired properties has no far been obtained.